Stress reducing inner sleeve for twist beam and associated method

ABSTRACT

A twist beam axle assembly includes a twist tube and a tubular sleeve. The twist tube has a deformed portion with a non-circular cross-section positioned adjacent to an undeformed portion with a substantially circular cross-section. The tubular sleeve is positioned within and coupled to the twist beam to overlap the adjacent deformed and undeformed portions. An outer surface of the sleeve engages an inner surface of the twist tube.

BACKGROUND

The disclosure relates generally to vehicle axles. More particularly,the present disclosure relates to a twist beam axle assembly having areinforcement sleeve used to improve the stress gradient within thetwist beam.

Twist beam axle assemblies typically function to transfer the vehicleload through rotatable wheels. The twist beam axle typicallyinterconnects two suspension components such as trailing arms that notonly rotatably support the wheels but also function to isolate one wheelof the vehicle from the opposite wheel. The suspension components mayinclude body mounts, wheel spindles, torsion bars, shocks and springs.The twist beam axle may include trailing arms, spring mounts, shockmounts and spindle flanges, among others, to interconnect the varioussuspension components.

The twist beam axle assembly functions not only to transfer the vehicleload to the ground via the rotatable wheels but also provide desirableriding and handling characteristics as well as proper wheel tow andcamber. Previously known twist beam axles typically include U-shaped orV-shaped beams oriented to be relatively rigid in bending but relativelycompliant in torsion. These twist beam axles typically include manybrackets at each end of the beam to couple the beam to trailing arms orother suspension components. Furthermore, typical twist beam axlesprovide a torsional stiffness of approximately 350 N-m/degree. Whilebeams having this torsional stiffness have functioned, it may bedesirable to provide an increased torsional stiffness of approximately800-900 N-m/degree. Providing a twist beam axle with a relatively hightorsional stiffness may present a challenge due to the local stressesintroduced at the interconnection of the twist beam and the trailingarm. Accordingly, it may be beneficial to provide a twist beam axleassembly having a reinforcement sleeve to reduce the magnitude of localstresses found near the interconnection of the beam and the trailingarm.

SUMMARY

The present disclosure relates to a twist beam axle assembly including atwist tube and a tubular sleeve. The twist tube has a deformed portionwith a non-circular cross-section positioned adjacent to an undeformedportion with a substantially circular cross-section. The tubular sleeveis positioned within and coupled to the twist beam to overlap theadjacent deformed and undeformed portions. An outer surface of thesleeve engages an inner surface of the twist tube.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is perspective view of a twist beam axle assembly according tothe teachings of the present disclosure;

FIG. 2 is a fragmentary perspective view of the twist beam axle assemblyshown in FIG. 1;

FIG. 3 is a cross-sectional view taken through a deformed portion of thetwist beam axle assembly;

FIG. 4A is a perspective view of components of the twist beam axleassembly prior to deformation;

FIG. 4B is a fragmentary perspective view depicting a deformationprocess;

FIG. 5 is a fragmentary perspective view showing a weldedinterconnection between a reinforcement member and a beam;

FIG. 6 is a cross-sectional view taken through a laser weld;

FIG. 7 is a fragmentary perspective view depicting a portion of anothertwist beam axle assembly; and

FIG. 8 is a perspective view of another reinforcement member for usewith a twist beam axle assembly.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

FIGS. 1 and 2 depict a twist beam axle assembly 10 having a firsttrailing arm 12, a second trailing arm 14 and a twist tube or beam 16interconnecting the trailing arms 12,14. Trailing arms 12,14 may beconstructed from a cast iron material. Beam 16 may be constructed from ahigh strength steel such as 22MnB5. Beam 16 may also be constructed fromhigh strength steels including ferrite, bainite or martensite.

Trailing arm 12 is substantially a mirror image of trailing arm 14. Assuch, only trailing arm 12 will be described in detail. Trailing arm 12includes a cylindrically shaped central boss 20, an end boss 22, a firstflange 24 and a second flange 26. Central boss 20 and end boss 22 areinterconnected by a first rib 28, a spaced apart and substantiallyparallel second rib 30 and a third rib 32. Third rib 32 interconnectsfirst rib 28 and second rib 30. An aperture 34 extends through third rib32 to reduce the weight of trailing arm 12. Central boss 20 terminatesat a substantially planar face 35.

On the opposite end of trailing arm 12, first flange 24 and secondflange 26 extend substantially perpendicular to one another. A bracket36 supports first flange 24 and second flange 26. More particularly,bracket 36 includes first and second sidewalls 38,40 extending betweenfirst flange 24 and second flange 26. A center panel 42 interconnectsfirst sidewall 38 and second sidewall 40.

A rail portion 44 interconnects first sidewall 38 and central boss 20.Due to the relatively complex geometry of trailing arm 12, it isbeneficial to use a casting process to economically form this suspensioncomponent. Although not explicitly shown in the figures, it should beappreciated that trailing arm 12 is configured to connect to othervehicle components (not shown) at end boss 22, first flange 24 andsecond flange 26.

Beam 16 is formed from an elongated tube having a first end 50 fixed totrailing arm 12 at central boss 22. Beam 16 includes an opposite end 52fixed to trailing arm 14. Beam 16 has a substantially circularcross-sectional shape at ends 50, 52. A deformed portion 54 extendsbetween ends 50, 52. FIG. 3 is a cross-sectional view taken throughdeformed portion 54. Beam 16 is constructed from a material having asubstantially constant thickness wall 56. Within deformed portion 54,wall 56 follows a convoluted path where a first segment 58 of wall 56has a substantially semi-circular shape in cross-section. A secondsegment 60 and a third segment 62 are each shaped as lobes connected toopposite ends of first segment 58. A fourth segment 64 shaped as atrough interconnects second segment 60 and third segment 62. The overallcross-sectional shape of deformed portion 54 may be characterized as“U-shaped” or possibly “V-shaped.” This cross-sectional shape providesrelatively high bending strength while being relatively compliant intorsion.

FIG. 4 depicts a transition zone 70 where the deformed portion 54transitions into undeformed substantially cylindrically shaped end 50.End 50 includes an end face 72 spaced apart from transition zone 70. End50 is fixed to relatively rigid trailing arm 12. Within transition zone70, the relatively stiff deformed portion 54 transitions to acylindrical shape that is much more compliant in bending. Accordingly, astress concentration may be produced within transition zone 70. Todistribute stresses throughout beam 16, a reinforcement sleeve 74 ispositioned within and coupled to beam 16 at transition zone 70.

A method of manufacturing twist beam axle assembly 10 will now bedescribed. Beam 16 is initially formed as a tube having a substantiallycircular cross-section along its entire length. Reinforcement sleeve 74is also formed as a tube having a substantially cylindricalcross-section along its entire length. In the embodiment presentlydescribed, sleeve 74 has an open first end 76 and an open second end 78.It is contemplated that twist beam axle assembly 10 includes a secondreinforcement sleeve (not shown) positioned proximate trailing arm 14.Because the second reinforcement sleeve is formed and positioned in asubstantially similar manner to reinforcement sleeve 74, only onereinforcement sleeve and beam interconnection will be described indetail.

Reinforcement sleeve 74 includes an outer cylindrical surface 80defining an outer diameter slightly smaller than an inner diameterdefined by an inner surface 82 of beam 16. Second end 78 ofreinforcement sleeve 74 includes an end face 84 positioned within beam16 substantially parallel to and axially offset from end face 72. A tool85 maintains the axial position of reinforcement sleeve 74 relative tobeam 16. While reinforcement sleeve 74 is being restricted from axialmovement, a ram 86 is axially forced into contact with an outer surface88 of beam 16. Ram 86 includes a die surface 90 shaped to definedeformed portion 54. During translation of ram 86, beam 16 is deformedto have the cross-sectional shape previously discussed in relation toFIG. 3.

Ram 86 not only defines the shape of transition zone 70 but also deformsa portion 92 of reinforcement sleeve 74. During the time that thedeformed portion 54 is created, inner surface 82 of beam 16 is forcedinto contact with outer surface 80 of reinforcement sleeve 74. Ram 86continues to extend a predetermined distance to define a maximum depthof the trough formed at fourth segment 64. Subsequently, ram 86 isretracted from engagement with beam 16. At this time, reinforcementsleeve 74 includes an undeformed portion 100 having a substantiallycylindrical cross-section at second end 78 and deformed portion 92positioned at first end 76.

After ram 86 has been retracted, tool 85 restricting axial movement ofreinforcement sleeve 74 may also be retracted. Deformed beam 16 andreinforcement sleeve 74 are interconnected to one another at this pointin the process. However, an additional fastening process is envisioned.In one contemplated order of operation, beam 16 and reinforcement sleeve74 are transferred as a subassembly to a fastening station.Alternatively, reinforcement sleeve 74 may be fastened to beam 16 at thesame location where the deformation process is performed.

Reinforcement sleeve 74 may be fixed to beam 16 via a number ofprocesses including riveting, adhesive bonding, screwing and welding. Ifadhesive bonding is utilized, the adhesive is placed at the interfacebetween outer surface 80 and inner surface 82 prior to the deformationstep. The other types of fixation would most likely be performed afterthe deformation step is completed.

FIG. 5 depicts reinforcement sleeve 74 being fixed to beam 16 with aplurality of laser welds. A first laser weld 106 extends substantiallylongitudinally along outer surface 88 within transition zone 70. Secondand third laser welds, 108, 110, extend circumferentially along outersurface 88. Welds 106, 108 and 110 are positioned at relatively lowstress locations where outer surface 80 of reinforcement sleeve 74engages inner surface 82 of beam 16. FIG. 6 depicts a cross-section ofthe laser weld connection between beam 16 and reinforcement sleeve 74.As shown, the laser weld penetrates both beam 16 and reinforcementsleeve 74.

FIG. 7 depicts a portion of another twist beam axle assembly 200. Twistbeam axle assembly 200 is substantially similar to twist beam axleassembly 10. Accordingly, like elements will retain their previouslyintroduced reference numerals. Twist beam axle assembly 200 includes areinforcement cup 202 coupled to beam 16. Reinforcement cup 202 issubstantially similar to reinforcement sleeve 74 except thatreinforcement cup 202 includes a substantially planar wall 204 closing afirst end 206 of reinforcement cup 202. In similar fashion toreinforcement sleeve 74, after deformation, reinforcement cup 202includes a deformed portion 208 and an undeformed portion 210.Undeformed portion 210 includes a substantially circular cross-section.After deformation, reinforcement cup 202 may be fixed to beam 16 usingany of the techniques previously described in relation to couplingreinforcement sleeve 74 with beam 16.

FIG. 8 represents another reinforcement member 230. Reinforcement member230 may or may not have an end wall. Accordingly, reinforcement member230 may be open at both ends or closed at one end and open at theopposite end. Reinforcement member 230 includes an inner surface 232.Reinforcement member 230 extends further into deformed portion 54 ofbeam 16 than reinforcement sleeve 74 or reinforcement cup 202. Based onthe increased length of reinforcement member 230, a deformed portion 234may include the cross-sectional shape shown in FIG. 8. In particular, afirst portion 236 of inner surface 232 is forced into engagement with asecond portion 238 of inner surface 232. An end 240 opposite deformedportion 234 extends into end 50 of beam 16 such that end 240 ofreinforcement member 230 has a substantially circular cross-section.

Various beam and reinforcement member combinations have been discussed.It should be appreciated that other permutations of reinforcement memberand beam features in addition to those explicitly discussed arecontemplated as being within the scope of the present disclosure.Furthermore, while a rear axle twist beam interconnecting opposingtrailing arms has been discussed, the present disclosure may relate to anumber of other vehicle components including front axles, torsion barsand other suspension components. Similarly, the components connected tothe ends of the twist beam may be formed from any number of processesincluding sheet metal forming, forging, casting, and may includematerials such as aluminum, steel, and their alloys.

1. A twist beam axle assembly, comprising: a twist tube having adeformed portion with a non-circular cross-section positioned adjacentto an undeformed portion with a substantially circular cross-section;and a tubular sleeve positioned within and couple to the twist tube tooverlap the adjacent deformed and undeformed portions, wherein an outersurface of the sleeve engages an inner surface of the twist tube.
 2. Thetwist beam axle assembly of claim 1 wherein the sleeve includes a closedend to define a cup with an open end.
 3. The twist beam axle assembly ofclaim 2 wherein the open end of the cup is positioned to face an openend of the undeformed portion.
 4. The twist beam axle assembly of claim3 wherein a portion of the closed end is deformed to have a shapeconforming to the inner surface of the deformed portion of the twisttube.
 5. The twist beam axle assembly of claim 1 wherein one end of thetubular sleeve is deformed to cause a first portion of an inner surfaceof the sleeve to contact another portion of the inner surface of thesleeve.
 6. The twist beam axle assembly of claim 5 wherein an endopposite the one end of the sleeve has a circular cross-section.
 7. Thetwist beam axle assembly of claim 1 wherein the sleeve is coupled to thetwist tube by one of laser welding, riveting, threaded fastening andadhesive bonding.
 8. A method of manufacturing a twist beam axleassembly, comprising: inserting a tubular sleeve within a twist tube;deforming a portion of the sleeve and the twist tube such that an outersurface of the sleeve engages an inner surface of the twist tube alongat least a portion of the deformation; and fastening the sleeve to thetwist tube.
 9. The method of claim 8 wherein fastening includes at leastone of laser welding, riveting, adhesive bonding and screwing the sleeveto the twist tube.
 10. The method of claim 8 further including formingthe sleeve to include a closed end to define a cup with a bottom. 11.The method of claim 10 further including positioning an open end of thecup proximate to a distal end of the twist tube.
 12. The method of claim11 wherein deforming includes deforming a shape of the bottom of thecup.
 13. The method of claim 8 further including placing the sleeve on amandrel and fixing the position of the sleeve relative to the twist tubewith the mandrel during deforming.
 14. The method of claim 13 furtherincluding removing the mandrel from the sleeve and the twist tube afterdeforming has been completed.
 15. The method of claim 8 whereindeforming includes forcing one portion of an inner surface of the sleeveinto contact with another portion of the inner surface of the sleeve.16. The method of claim 8 wherein the sleeve and the twist tube havecircular cross-sectional shapes prior to deforming.
 17. The method ofclaim 16 wherein portions of the sleeve and the twist tube retain thecircular cross-sectional shape after deforming.
 18. The method of claim8 further including offsetting an end of the sleeve inwardly from an endof the twist tube prior to deforming.
 19. The method of claim 8 furtherincluding fixing one of first and second trailing arms to each end ofthe twist tube.
 20. The method of claim 19 further including inserting aportion of the first trailing arm within the twist tube prior to fixing.